1. Field of the Invention
The present invention relates to an apparatus and method for running dual cameras in a portable terminal. More particularly, the present invention relates to an apparatus and method for separating a sub camera path from a main camera path using a switch in a portable terminal.
2. Description of the Related Art
The use of portable terminals is rapidly increasing due to developments in various electronics and communications technologies. In addition to their main communication functions, portable terminals have been developed to support a variety of additional functions to meet users' demands. For example, portable terminals provide additional functions such as a phonebook, games, a short message service, an internet service, an e-mail service, a morning call, a file viewer, a file transfer, an auto response service, a camera service and various other functions.
As the number of additional functions combined into the portable terminal is increasing, the more complicated the organization of the portable terminal is becoming. Also, the performance of the portable terminal potentially deteriorates as the electronic components on the main board interfere with each other.
For example, as the camera resolution of the portable terminal advances from Quarter Common Intermediate Format (CIF) to Video Graphics Array, 1.3 Mega-pixels, 2 Mega-pixels and beyond, the clock frequency of the camera increases. Therefore, interference between components increases.
A portable terminal employing dual cameras, such as a main camera and a camera for making video calls, has been recently introduced. In such a portable terminal having dual cameras, there is also a tendency that the portable terminal will have a slim design. Moreover, the cameras have a high number of pixels. In this situation, the module of the camera is likely to be affected by noise and therefore may not work well. Also, as the number of camera pixels increases, the amount of data generated by the camera pixels increases, and therefore a faster main clock and pixel clock are needed. However, the faster clocks influence other circuits within the portable terminal.
In general, when the portable terminal executes, a camera operation, a main chip or a backend chip for display controls the camera. As part of the control, the main chip or the backend chip provides a main clock to a module of the camera. In turn, the module of the camera generates a pixel clock using the main clock.
Accordingly, unless the portable terminal includes a main chip or backend chip for display of a video call, the video call camera uses the same camera data path as the main camera. When the main camera operates, the data path of the video call camera affects the clock of the main camera and leads to improper functioning of the main camera.
FIGS. 1A and 1B are block diagrams illustrating an input clock signal to dual cameras in a conventional portable terminal. In the description below, a main camera is a general high-pixel camera and a sub camera is a video call camera.
Referring to FIG. 1A, a main chip 100 provides a main clock signal to the sensors of a main camera 102 or a sub camera 104. The main chip 100 receives a pixel clock signal from the main camera 102 or the sub camera 104. In the connection as used in the conventional art, the main camera 102 and the sub camera 104 share a common routing point 110 from the main chip 100.
As described above, if the main camera and the sub camera use the same path from the main chip, that is if they share a common routing point 110, a clock waveform of the main camera is subject to interference by the load of the sub camera. For example, as illustrated in more detail in FIG. 1B, the connection of the sub camera to the common routing point 110 results in a parasitic shunt capacitor (Ceq) which functions as a load on the main camera as described by Equation (1).T=R*Ceq Zin=2Π*f*Ceq   (1)
In Equation (1), T denotes a rising time of a clock signal, Zin denotes an input impedance, R denotes a resistance, and f denotes a clock frequency. As is evident from Equation (1), the rise time T changes by the magnitude of the shunt capacitor of the sub camera and Zin increases in proportion to the magnitude of the shunt capacitor of the sub camera and the frequency of clock.
In a conventional arrangement, the sub camera may be positioned on a sub body and the main-camera may be positioned on a main body in a slide type portable terminal. When the sub body slides to the operating position, a length of a clock path of the sub camera between the main chip and the sub camera increases. Accordingly, unless the portable terminal includes a backend chip, the size of the shunt capacitor load would be larger according to the length of the connection path and a problem may occur such as a collapse of the clock waveform or a pixel error. Accordingly, a need exists for an apparatus and method for operating dual cameras in a portable terminal.